There's no reason why subfig should be deprecated. Of course it's alternative to subcaption.
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egregSep 2 '12 at 15:18

I dont know, @egreg, but from the TeX Catalogue in Line: This package [subfig] supersedes the subfigure package ... The functionality of the package is provided by the (more recent still) subcaption package. (I known... newer is not a solid reason, but ask to Google).
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FranSep 2 '12 at 16:23

subfig and subcaption are just two packages that do similar things with different approaches.
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egregSep 2 '12 at 16:52